Mechanically-actuated diaphragm-horn.



M.R.- HUTCHISON.

MECHANICALLY ACTUATED DlAPH'RAGM HORN.

7 APPLICATION FILED JULY'Q. l9l0.

Patented Nov. 16, 1915.

2 SHEETS-SHEET I.

V/VW

human srars rrrr ore MILLER REESE HU'I'GHISON, OF NEW YORK, N. Y., AsSIGNOB, TO LOVEIiIr-MGCONNELL MANUFACTURING COMPANY, A CORPORATION OF DELAWARE.

MECHANICALLY-ACTUATED DIAPHRAGM-HORN.

'-vented certain new and useful Improvements in lVIechanically-Actuated Diaphragm- Horns, of which the following is a specification.

The improvements referred to are embodied in the automobile'warning signal set "forth in my prior application, Serial No.

494,120, filed May 5th, 1909, or which this application is a division.

They relate tocam operated diaphragm horns of the type set forth in my prior applications, Serial No. 305,933, filed March l lth, 1906 and Serial No. 373,946, filed May 16th, 1907, (granted May 25th, 1909, as Patents Nos. 923,048, 923,049 and 923,122) which were co-pending with my said application of which this application is a division.

They consist of certain important features of construction and operation whereby the basic principles set forth in said earlier application have been rendered practically useful and commercially successful.

In said earlier co-pending applications, I disclosed certain devices and generic methods of producing sound by causinga thin steel diaphragm of suitable proportions to execute bodily vibrations, bowing as a whole first on one side of its neutral or normal plane and then on the other, by means of a rotary cam having cam projections of low much more disagreeable, penetrating sound pitch, spaced widely apart, and rotated at speed harmonizing with the natural times of the outward swing of the diaphragm.

The sound thus produced. consists mainly of a music like note consisting of the alternately rare and dense waves of air generated by the unitary vibration or bodily swing of the diaphragm as a whole. This note is very easily distinguishable from the effect produced by. concussion ripples of the diaphragm due to violent impacts when the latter are not timed so as" to promotethe naturaLswingabove referred'to. My said co-pen'ding applications disclosed fully how a device of this kind may be continuously operated to produce sound by this harmoni- Specification of Letters Patent. 'Patented Nov. 16, 1915.

Original application filed May 5, 1909, Sen'aI No. 494,120. Divided and this Serial No. 571,188.

application filed July 9, 1910.

ous or bodily swing method but in the said applications, I nowhere contemplated or provided forthe practical ilifiiculties in the way of using such devices for intermittent short signals Which are most in use where the devices are used for my primary purpose of automobilewarning signals.

For a commercially successful signal, it is not sufiicientto harmonize the cam contacts to every second or third or fourth natural swing of the diaphragm. There must be a cam push for every natural swing. The. only way to get a substantial amplitude of the bodily movement at lower speeds, is to make the path of the cam projections greatly overlap the rest position of the diaphragm wearpiece so as to force a full outward movement of the diaphragm at every cam contact. This heavy over-lap arrangement which is the one disclosed in my said Patents Nos. 923,08 and 923,122 gives the desired note at the harmonized speeds but the power required at non-harmonizing speeds is many times that required at the higher harmonizing speeds. Hence it is necessary to have some means of applying great power initially and reducing the shown in Patents Nos. 923,048 and 923,122,

or equivalently relaxing the push on the foot pedal or the pull on the chain shown in 923,0at9. Consequently, while mysaid prior devices are theoretically and to some eatent practically operable to produce a note by the harmonious body swing method, they are none of them adaptedfor the purposes of a commercial automobile Warning signal requiring brief, intermittent, instantaneously efiective operation Without special attention or skilled manipulation by the operator.

As aresult of the above and other defects in my prior devices, it was difficult to get diaphragms that would stand up a reasonable length of time during commercial op eration. with commercial devices which I put upon the market in the form shown in my Patent No. 923,049, whether with the heavy overlap described as preferred or with the light overlap described as capable of being utilized so as to give results, the operator in the excitement caused by immincnt danger, would press upon the foot pedal or pull on the .chain, with great violence so that the friction wheel would not the diaphragm became heated above the point where the temperof thesteel was destroyed. lVith this understanding of the difiiculties to be overcome my present invention will be readily understood. Itinvolves, among other things, devising a motor and energizing means, which are too'feeble to permit the heavy overlap of cam and wearpiece; then adjusting the cam with such slight overlap that no very powerful swing and reaction of the diaphragm will be built up until the full speed giving acam push for every swing, has been reached. Themotor should accelerate rapidly from a state of rest to the desired full speed so that there is no oppor tunity for building up a wide diaphragm swing at any of the nonharmonious lower speeds. I prefer an electric motor having an armature of greater diameter than the cam, so as to give powerful initial torque and the required rapid acceleration from rest to full speed. In this combination I prefer to use a cam of progressively increasing or accelerating pitch toward the tips so that some concussion sound may be produced by the steep pitch engagement of the tips of the cams with the wearpiece during acceleration, when bodily movement of the diaphragm is at minimum. Yet, when the full speed of push for every swinghas been reached, and the cam is engaging the diaphragm in the rearward bowed position where it is nearly stationary, the engaging cam surfaces will be of much lower pitch. The faces of the cam from this point of initial engagement onward to the tip are adapted to follow up the diaphragm and add increments to its outward movement throughout all the naturally accelerating portion of the swing and beyond the normal or rest position where acceleration naturally ceases, it leavesthe diaphragm substantially free to execute its natural outward movement and its rearward elastic return behind the normal rest position.

In my present device, I still prefer'to use the durable diaphragm materials. and construction of the generaltype disclosed in iny Patent 923,049 but by my present invention where wide diaphragm swing-'is attained only at harmonious speed, the diaphragm materials and construction may be very inferior without rendering the device uncom- Minor features and objects of my invention useful in the connections shown and in analogous relation will be evident from the detailed description of my invention.

From the above full description of the nature and objects of my invention, a concrete embodiment illustrated in the accom panying, drawings will be readily understood from said drawings, 'in which- Figure 1 is a vertical central section of the horn and motor assembled, the battery connections being diagrammatically indicated; Fig. 2- is a central transverse section at r1 ill] angles to the plane of Fig. 1; Figs. 3 and l are detail views of plane faced rotary cams; and Fig. 5 is a diagram illustrating rotary cam and diaphragm relations.

The general organization of the parts is shown in Figs. 1, and-2. The diaphragm 1 is clamped at the edges between two sections of aninclosing case. The rear section 2 is formed with rear walls approximately par- .allel with the diaphragm, except where it is enlarged, as at 3 and l, to form inclosing chambers for the cam, cam shaft, and bearings. The front face is formed with an annular clamping surfac'x5. The front cover or resonator section (3 of the diaphragm case.

is parallel with the diaphragm and far enough away from it to permit maximum v1- bration of the diaphragm without engagment with the case. It is formed with the central opening 7 of largediameter so as to expose a large part of the effectively vibrating part of the diaphragm. The opening is surrounded by an annular flange 8, which may be flared toward the open end; as indicated at 9. The resonator 10 is secured to this flange preferably by spinning the material against the outer wall thereof or by brazing or by both. The periphery of 6. is formed with a flange 11 fitted over the rear section 2 of the diaphragm case. As shown in the drawings, the clamping surfaces are of ample width and thickness to apply the clamping pressure of the screws 12 evenly about the periphery of the diaphragm. The quality of the note is improved and destructive vibration and cutting action of the diaphragm is prevented'by washers l3 and 14: arranged between the diaphragm and the clamping faces of each section .of

the case.- These washers may be of nonvibratory material such as cork, wood, or The diaphragm 1 is prohardened fiber. vided with a wear piece 15 formed with a shank 16 riveted over a Washer 17. By reference to Figs; 1 and 2 it will be seen that this wear piece is somewhat similar to that set forth in my prior Patent No. 883,643. The wear surface, however, is integral therewith and projects sufficiently so i that it may be hardened while the rivet portion is maintained in an annealed condition. This wear piece is formed with its wear surfaces transversely of the direction of rota tion of the cam and the surfaces are symmetrical in both directions.

' of the diaphragm case is formed with webs 18, 19, having alined openings for support of the cam shaft 20. The latter is mounted in a bearino sleeve 21 with its axis eccentric to but preferablyparallel with the axis of said bearing 21, as shown more clearly in Fig. 2. When said bearing is rotated, the

axis of the shaft moves in a circular path approximately parallel with the axis of the sleeve. In practice, I find that the radius of this eccentricity need not'be' much greater than the amplitude of vibration of the diapositionof longitudinal adjustment by phragm, in order to give a throw amply sufficient for all required adjustment of the cam shaft with respect to the diaphragm. T i'e sleeve bearing 21 is held in a desired means of the screw collar 22 engaging the .end \vall'of the casing This collar is locked in position by means of a screw key 23,

. screw threaded into collar 22 and having a stud24 engaging a recess in sleeve 21. There isa vcooperating lock nut 25 outside of the casing.- which may be loosened to permit rot'ary adjustment of the sleeve bearing 21 and the cain shaft 20 carried thereby and which {nay be tightened to rigidly clamp said bearing against both longitudinal and rotary movement. The cam 26 is keyed to the cam shaft 20 by pin 27 and is clamped againstshoulder 28 by locknuts 29.

, latter LIpOIIJSlBBXE'. 21.

' Oil for lubricating the shaft 20 and also the contact between cam 26 and weary piece 15, is supplied through an oil. passage or reservoir 30.. Part of the oil is thrown by centrifugal force from the rapidly revolvingcam against the projection 15 and part of it finds'its wav through the opening 31 arranged longitudinally of the shaft 20 and bearing sleeve is slightly eccentric thereto, as indicated at 81, though this eccentricity may be so small as to be practically. un-' noticeable to the eye from the exterior The end of the sleeve 21 is formed as an end wall 35 of the motor case 33 and is secured to the latter by screws 36, 36. On the cam shaft 20 is mounted the motor armature 37 revolving between pole pieces 38, 38, formed as integral projections of the shellor case 33 and energized by field windings 39, 39. The case 33 is closed in at the bottom by an inclosing wall 4L0 formed with a journal 4-1 for the lower end of shaft 20. Surroundv 1,iso,sea

The section 2 ing this is an annular cavity 42, supplying 4 lubricatingoil or greas'ethrough passages 4-3. The lubricant is held in position by means of a disk 44, engaging the annular shoulder 15. The current'for operating the motor is derived from battery 46 controlled by circuit. closers, as at 17, and, if desired, regulated by an adjustable resistance E. This circuit is connected tobinding posts 48, 18, leading within the case-33 and'insulated therefrom by bushings 19, 19. As diagrammatically indicated by dotted lines in Fig. 1, the current is supplied in parallel to the field windings 39, 39 and to the brushes 50, 50 of commutator 51 su lying armature 37. Above the armature 3%, upon the armature shaft 20, adjacent the end of sleeve 21, is arranged a collar 52, whereby the drip of excess oil is thrown off centrifugally on the sides of the case 33 and so is prevented from saturating the armature and leaking down on the commutator, thereby impairing the contact of the commutator bars therewith.

. By reference particularly to Fig. 2, it will be seen that the adjustment of the cam shaft to and from the diaphragm may be accomplished'by rotating the eccentric sleeve 21 through a quarter rotation in either direction from the medial position shownin said Fig. 2 and that rotation through a. semi-circuznference from said position will bring the axis of the cam shaft to a position where it is exactly the same distance perpendicularly from the diaphragm, but is on the left hand side of the axis of sleeve 21. In certain cases, it is confusing to unskilled users to have an adjustment of this kind wherein a continuous rotation in one direction acts as an adjustment toward the diaphragm through a half revolution, and then as an adjustment away from the diaphragm during the other half revolution. I may avoid this by arranging the seats 60, 61, shown in dotted lines in Fig. 2, adjacent the collar 22 so as to be engaged by the head of screw .23, "thereby limiting the rotary adjusting may be permitted to extend through normal and to a desired distance beyond normal, so that the kinetic energy of the high velocity return movement will be usefully expended in storing up potential energy in the form of elastic stress. In actual practice, I find thatwhere this timing is accomplished by proper spacing, altitude, and speed of the cam projections with respect to the power of the motor, the rotary cam need not have carefully designed curved faces, but may be formed as true straight line planes, as shown in Figs. 3 and 4. In Fig-3, the operative faces on the advancing sides of the cam projections are formed as plane surfaces.

Each surface 7 0 is for convenience cut back so as to form an abrupt, approximately radial shoulder 71 in the rear. of the next adj acent cam projection so that the contour of the cam somewhat resembles a ratchet wheel with the tips of the ratchet teeth ground ofi. The tips are ground off not so much for the purpose of making the rotor periphery concentric with the shaft but rather for the purpose of providing flat surfaces for impact of the diaphragm wearpiece at nonsynchronou's speeds, the violence of these impacts being such that it is difficult to find materials capable of withstanding them if the tips are left sharp. If hard enough not to be deformed by the blows the material is apt to crumble and if soft enough not to crumble, is apt to deform. In actual manu-- facture, the plane surfaces 70, are cut in the periphery of the rotary cam by an ordinary milling machine. The material is then tem pered. This results in some deformation, which, in practice, is sufliciently corrected by grinding off the tips of the projections, as at 72, so that the periphery is accurately centered with respect to the axis of the cam shaft.

In Fig. 4:, the plane milling is carried through so that no shoulders are formed as in Fig. 3, the periphery being a regular polygon. In a compact portable device, such as herein disclosed, the desirable diameter of cam islimited to some extent by the comparative inefficiency and feeble torque of the armature when the current is first turned on, and, in most cases, where a polygon of such limited diameter is used, I prefer an octagon, such as shown, though polygons of from 'five'to twelve sides have been used successfully. In Fig. 3, there are ten cam.

projections, but the effective cam pitch of each projection corresponds to the pitch of the points of a regular hexagon.

In practice, I prefer to make the diaphragm and the wear piece thereon light in weight, thereby decreasing inertia as far as may be consistently w th the requirements 55 of stiffness and durability. The diaphragm is preferably of fine quality rolled steel, such as vanadium nickel steel, and may be used either tempered or annealed, though the tempered diaphragm gives a better note. A resonator associated with the diaphragm tends to govern the frequencies of the diaphragm as well; as to amplify and reinforce the movements when they are of the same frequency as one of the resonant frequencies of the resonator, and I prefer to use a resonator having an air column equal toat least 1,ico,eee

a half wave length of the normal operating frequency of the rotary cam contacts. The.

air column should have a diameter at the base sufficient to extend over substantially all of the freely vibrating parts of the diaphragm so as to receive large amounts of energy from the diaphragm and also to react upon the diaphragm with strong resonant effect, thereby tending to hold the diaphragm and through it the cam and motor to the resonant frequencies-slightly above the natural frequency of free bodily vibration of the diaphragm, throughout wide variations of power'. Hence, I make the diameter of the base of the resonator between one-third and two-thirds of the unclamped part of the diaphragm. It is preferably flared toward the open end so as to spread the sound and to modify and enlarge the mobiles is a direct current shunt wound motor adapted to drive the rotary cam at about 450 revolutions per second when operating on five to seven volts, and preferably capable of taking 12 to 20 volts for periods of ordinarv use without damage to the windings.

Fig. 5 is a diagram showing that in a rotary cam with plane cam surfaces of relatively great peripheral extent, the effective operative pitch in respect to the wearpiece of the diaphragm is accelerated or progressively greater toward the tip. The cause of this is the changing relation of the straight line face with reference to the wearpiece of the diaphragm, as the cam surface rotates past the same. The amount of the acceleration due to this cause, will depend upon the circumferential angle through which the cam face extends rather than upon the physical size of the cam or of cam faces.

Hence by selecting a suitable circumferential desired acceleration of the pitch toward the tips for purposes hereinafter referred to. In said Fig. 5 the plane cam face a, b, corresponds to half of one side of a polygon circumscribed about an are a, c, of a circle having its center at (Z. The are a, 0 represents the effective base of the cam projection, the radial'distance 0, 5 being the effective altitude. The rate of increase or acceleration of the operative pitch of the plane surface a, 1)

as it travels past the wearpiece on the diaphragm corresponds to the increasing altitudesalong the lines 6, f, g, h, 2', etc. In this case the are a, 0 through which the cam face extends is a very considerable one and hence departs very materially from a straight line so that the effective pitch of the cam, instead of being uniform from a, c as might be imagined from its straight line form is in fact of steadily and'very materizillyincreasing pitch toward the tip. In order to show more clearly to the eye, the rapidity of this acceleration .of pitch toward the tips, I have shown in the upper part of the diaphragm an equivalent cam with the same'base, altitude and rate of change of pitch but the base is astraight line instead of an arc and the movement is a longitudinal movement lengthwise of said straight line instead of a circular movement endwise ofthe circular line a, c. The linear speed of the base a c is supposed to be the same as the peripheral speed of the base a, 0 so that the operative rate of change of pitch of the respective altitude e, f g, h i, is the same as that of e, f, g, h, 2'. By considering the cam pro jection a, b, c as the equivalent of the rotating projection a, b, c and by assuming the relative movement of cam and diaphragm to consist of a lateral movement of the diaphragm along the cam, instead of vice versa, it is'possible to indicate some-of the impor tant relations diagrammatically, as, for'instance, some of the eifects of change of speed, spacing, and adjustment of the cam projections relatively to the diaphragm. For this purpose, I have associated with the cam a b c a straight line 71:, Z along which the wear piece of a diaphragm projection, such as 15, Fig. l, is supposed to move in the direction of the arrow at a rate equal to a given peripheral speed of the cam projection (1,12, 0.

In .order' to show several relations in a small diagram, I have considered the diaphragm as already in vibration and at the top of the outward swing away from the cam at the instant it passes the point m. The lateral movement parallel with the line 1 combined with the vibratory movement projection to describe a wave line curve,

ing parts, and, in general, the characteristies are exaggerated, the purpose being merely to show some of the operating factors which are involved in transverse bodilyvv vibration of the diaphragm and also some-- 'thing of their relation to the cam. Some of the principal factors involved are as follows: The transverse movement of the diaphragmtoward normal from mto n is a the diaphragm, causes the diaphragm" from m to 0. It will be evident from the diagram that "the amount of power required will be sub ject to considerable variation according to the particular point in the cycle of vibration at which the cam intercepts the diaphragm contact. In general, it will be seen that where this occurs so that the initial engagement of the cam takes place after the dia phragm has already commenced its outward movement, the forced movement is added to the elastic movement and all of the power of the cam is utilized in doing useful work on the diaphragm. this is true for all points of interception lying between 0 and go. If, however, the point of interception is in advance of 0 and between it and n, the work done by the cam includes checking the inward movement of the diaphragm as well as supplying the power for forcing the outward movement. In case the point of interception is not much in advance of the innermost position, the inertia to be overcome in checking the diaphragm will be small and the reverse elastic stress available for assisting the outward forcing movement of the cam will be reat. For instance, in the case of'the cam?) intercepting the inward swing of the diaphragm at s, the amount of power wasted is small because the velocity of the diaphragm at that point is small and most of the power of the inward movement has already been stored up in the form of reverse elastic stress. Hence, in practice 8 is a very good point for the cam to intercept the natural rearward swing of the diaphragm. If, however, the speed of relative movement of the diaphragm and cam be increased or the projections be spaced. more closely to each other, so that the cam surface 72 intercepts the diaphragm at a point much in advance of e, the work to be done increases very rapidly, because of the increasing power required to check the inward movement of the diaphragm and the decreased elasticity available to assist the outward movement, When the interception occurs at the point 11, all of the energy of the return movement of-thediaphragm acts n, direct opposition to the cam. Moreover, the diaphragm being then at normal, there is no reverse elasticity to assist the outward movement. Thus my practical device may its 90 It will be seen also that be designed and adjusted for a certain critical range of speed where slightly increasing the speed of agiven rotary cam increases the work done by the cam, by cutting short the movement of the diaphragm below normal, by increasing the velocity at which the diaphragm contact leaves the summit of the rotary cam projection, and'by increasing the number of cam contacts per unit time. For these reasons, motive power sulficient to maintain a speed necessary for a 'given note with the diaphragm intercepted by the cam at orbehind the point 8, is entirely inadequate to maintain the same note with the diaphragm intercepted at 1'. Conversely, considerable variation in the voltage of the current supplied to the motor causes a relatively small change in the note of-the horn. The diagram also makes evident that adjustmentof the cam toward the diaphragm may be used to harmonize the diaphragm and cam movements for a'given suitable power and speed of motor, and that if the ad ustment be extended beyond a certain point, it f tends to cut short the power saving part of the inward swing of the diaphragm and that it also tends to force the swingmore and more in the region beyond normal where the elastic tension of the diaphragm is greater and the forced movements require more power. o

The general principles of s aclng, speed,

and adjustment as explained a ove with refis attainable by mechanically harmonizing the cam forcing movementsto the natural swing of the diaphragm; second, it. shows that for practical harmonizing the point 8 is almost as good a point for the cam to intercept the diaphragm as are the extreme rear-most points 0 and t and third, it shows how and why I have been able to succeed in actually establishing points corresponding to 's as the practical upper limit of normal full speed operation of my commerclal device, so that all instruments of the same model produce the same characteristic note of substantially the same pitch notwithstanding the wide variations of internal friction and battery strength attendant upon practical commercial use.

In practice, it will be found that with my above described designs of*cam-, diaphragm,

wearpiece and motive power, the instrument may be standardized for the desired normal full speed operation by having the cam tips very slightly overlapping the normal equilibrium position of the diaphragm wearpiece. The precise degree of such slight overlap canbest; be determined by practical test. The locknut 25 is loosened and the curlimit the operation so as to utilize the full amountof power required to speed up the motor through the frequencies where harmonious operation. is impossible and to maintain the uniform or standard high frequency producing the uniform or standard body swing note generated by the greatly amplified body swing of the diaphragm on both sides of normal.

While I have herein fully shownand described,- and have pointed out in the appended claims certain novel features of construction, arrangement, and operation which characterize my invention, it will be understood by those skilled in the art that various omissions, substitutions, and changes in the forms, proportions, sizes, and details of the device and of its operation, may be made without departing fromthe spirit of my invention.

The specific structural details whereby the motor and driveshaft are adjustably connected with the rear casing of the instrument are independent of, though usable with, my present invention, and the specific claims for such details are contained in my co-pending application SerialNo. 494,120, filed May 5, 1909, of which this application is a division.

Herein, I claim:

1. A horn or signaling device including a' diaphragm, a wearpieceand' a rotary .cam

having a pluralitypf plane peripheral cam faces, each extending through a considerable circumferential angle so that its effective pitch with reference to the diaphragm wearpiece is materially accelerating toward the tip by reason of its rotary movement through such angle, the position of-said rotary cam I being predetermined or adjusted so that the rotary path of the cam tipsvery slightly overlaps the normal rest position of the diaphragm wearpiece, whereby the accelerating-pitch portions of the cam operate substantially in the region of naturally accelerating outward movement of the freely swinging diaphragm, in combination with means for driving said cam only in the proper direction to. utilize sai plane faces as the operative faces of said cam. l 2. A horn orsignaling device including a diaphragm, a wear-piece thereon, and a rotary cam having a plurality of plane pe- I at approximately concentric peripheral tips, the position of said rotary cam being predetermined or adjusted sothat the rotary path of the cam tips very slightly overlaps the normal rest position of the diaphragm wearpiece, whereby the accelerating-pitch portions of the cam operate substantially in the region of natu rally accelerating outward movement of the freely swinging diaphragm.

3. A horn or signaling device including a diaphragm, a wear-piece thereon and a rotary cam having a plurality of plane peripheral cam faces, each extending through a considerable circumferential angle so that its effective pitch with reference to the diaphragm wear-piece is materially accelerating toward the tip by reasons of its rotary movement through such angle, the position of said rotary cam being predetermined or adjusted so that the rotary path of the cam tips very slightly overlaps the normal restposition of the diaphragm wearpiece, whereby the accelerating-pitch portions of the cam operate substantially in the region of naturally accelerating outward movement of the freely swinging diaphragm, in combination with an electric motor designed and energized so as to start said cam and drive it up to a speed but slightly greater than the natural frequency of the swing of the diaphragm, but not to over-balance the reactive energy of the diaphragm swing rearwardly of its normal rest position at that frequency.

4. An alarm or signal comprising a thin elastic steel diaphragm, clamped about its edges and adapted to produce a continuous note by free bodily swings on both sides of its neutral or normal equilibrium position its natural fundamental frequency, a rotary cam having a plurality oflow-pitch, direct-acting, cam projections adapted to apply a direct outward thrust to the diaphragm, the space between said cams being of sufiicient depth to permit free inward swing of the diaphragm rearwardly of itsnormal equilibrium position, an electric motor having an armature shaft on which said cam is mounted, the overlap of cam projections and diaphragm wear-piece being shght and predetermined in respect to the power of the motor for the purpose and "with the result of producing only small amplitude vibrations of small power at subnormal speeds, but building up Wide amphtude swings on both sides of normal equilibrium at a speed giving cam contacts at frequencies slightly above the natural fundamental frequency of the diaphragm,and means for energizing said motor sufficiently to drive the cam up to said latter speed, but insufficiently to overcome the thus amplified power of the diaphragm swings rearwardly of normal, the latter acting to limit and determine the normal speed of the motor,

"substantially as described.

5. In a device for producing an alarm or warning signal of the class described, a thin elastic steel diaphragm, provided with an attached wearpiece, said diaphragm being clamped about its edges and having its central portion adapted to swing bodily on both sides of its neutral or rest position at a fairly definite natural rate or fundamental frequency, a rotary cam having a plurality of substantially similar, low-pitch cam proj ections designed and arranged to apply outward thrusts perpendicularly to the diaphragm, thespace between the operative cam surfaces being of sufficient Width and depth to permit natural inward swing of the diaphragm rearwardly of its neutral or rest position, said parts being positioned with butslight/overlap of the rotary path of the cam tips in reference to the neutral or rest position of the diaphragm, in combination with a serially arranged circuit, circuit closer, battery and rotary electric motor having said cam on the armature shaft thereof, said motor and battery being designed, upon closure of said circuit, to give a predetermined power output sufficient to start said cam and drive it up to a speed where the cam contacts occur at a frequency slightly greater than said natural fundamental frequency of bodily swing of the dia- I phragm, but not sufficient to overcome the amplified reactive energy of; the natural swing of the diaphragm rearwardly of its neutral or rest position due to operating at said frequency, thereby determining said speed and frequency of cam contacts as the normal for full speed operation of said warning signal, for the purpose described.

Signed at New York city, in the county of New York, and State of New York, this seventh day of July, A. D. 1910.

MILLER REESE HUTGHISON.

lVitnesses:

GEORGE C. DEAN, IRVING M. OBRIEGHT.

Gopies of this patent may be obtained for five cents each, by addressing the Commissioner of Patents, Washington, D. G. 

